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Internal alignment between Filtergram (FG) and Spectro-Polarimeter (SP), image scale. T. J. Okamoto (NAOJ/Kyoto Univ.) Y. Katsukawa, T. Shimizu, K. Ichimoto, Y. Suematsu, S. Tsuneta, T. Tarbell, and SOT team. Abstract. We examined the relative alignment among the instruments on SOT.

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Internal alignment between filtergram fg and spectro polarimeter sp image scale

Internal alignment between Filtergram (FG) and Spectro-Polarimeter (SP), image scale

T. J. Okamoto (NAOJ/Kyoto Univ.)

Y. Katsukawa, T. Shimizu, K. Ichimoto, Y. Suematsu,

S. Tsuneta, T. Tarbell, and SOT team

Abstract

  • We examined the relative alignment among the instruments on SOT.

  • --- with a test data set obtained in the natural sun-light test in May 2005,

  • --- to an accuracy of better than 0.1 pixel corresponding to 0.02”.

  • It is important to know relative displacements and plate scales of these

    instruments for accurate alignment of observational data.


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Overview Spectro-Polarimeter (SP), image scale

The main contents in this presentation are the following:

1. Relative alignment of Filtergram (FG) images

a. Displacements and plate scales among Broadband Filter Imagers (BFIs)

and Narrowband Filter Imagers (NFIs)

b. Dependence on focus position

2. Relative alignment of Spectro-Polarimeter (SP) Images

a. Displacements and plate scales between SP and NFI

b. Uniformity of scanning steps

FG

SP

BFI

NFI

alignment

5550

5576

3883

4504

5172

6302

6302

3968

6684

5250

6563

4305

5896

(Angstrom)


Internal alignment between filtergram fg and spectro polarimeter sp image scale

1(a). Relative alignment of FG images Spectro-Polarimeter (SP), image scale

The grid pattern was located at the secondary focus of the simulated

Optical Telescope Assembly (OTA).

The images of the pattern were taken through all the filters of FG.

We measured positions of all the crosses in the grid pattern, and derived relative displacements and plate scales.

FG image (BFI)

1024

pix

2048 pix

overview

FPP

Re-imaging lens

grid

Solar light

CLU

(Collimator Lens Unit)

Pinhole-array


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(BFI)

E

BFI images

  • Determine grid positions for each filter

  • Plot relative displacements of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image

N

CN bandhead 3883

blue cont 4504

green cont 5550

Ca II H line 3968

G band 4305

red cont 6684

y

1024

pix

x

2048 pix

(Focus = 2009)

(date = May 26)


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(BFI)

  • Determine grid positions for each filter

  • Plot relative displacements of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(BFI)

  • Determine grid positions for each filter

  • Plot relative displacements of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image

  • These shifts are due to wedge of each filter.

  • (because only filters are different in the

  • optical system)

  • This can be easily corrected.


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(BFI)

  • Determine grid positions for each filter

  • Plot relative displacements of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image

wavelength-dependent image shift (averaged) removed

color aberration

difference of plate scale


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(BFI)

  • Determine grid positions for each filter

  • Plot relative shifts of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image

color aberration (difference of plate scale)

X-axis

Y-axis

Grid position displacements

Grid position displacements

Grid position in X (pix)

Grid position in Y (pix)

Relative plate scale

As the wavelength is longer, the plate scale is smaller.


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(NFI)

wavelength-dependent image shift (averaged) removed

The grid images taken with NFI were processed with the same procedure as with BFI.

Average displacements

Relative plate scale

Similar to BFI, as the wavelength is larger, the plate scale is smaller.


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(between BFI and NFI)

The relative displacement of central grids of BFI 5550A with respect to NFI 5576A.

BFI

NFI

The relative plate scale among the images of BFI (5550A) and NFI (5576A).

0.6732 (designed: 0.6750)

!!! Remaining issue: absolute plate scale


Internal alignment between filtergram fg and spectro polarimeter sp image scale

1(b). Alignment depending on Focus Position Spectro-Polarimeter (SP), image scale

The following figures show the displacements of the grid points in the X-direction as a function of the focus positions. The displacements represent the shifts from the grid positions obtained at focus position 2009. The images taken with BFI 5550A and NFI 5576A are used here. Only the grids in the middle row are plotted in these figures.

  • We notice 2 features from the figures:

  • periodic variations with an amplitude of several pixels in a period of 18.

  • change of plate scales: the distance between two grids of the images becomes smaller as the focus position is larger. This means the plate scale is larger at the larger focus positions.

BFI

NFI

right

left

(arbitrary position)

This variation is due to change of shift of lens as the position of focus is moved. However, it is regardless because it is rarely moved during observations.

(it is needed to correct the alignments again when we adjust the focus)


Internal alignment between filtergram fg and spectro polarimeter sp image scale

2. Relative alignment of SP images Spectro-Polarimeter (SP), image scale

We examine the plate scale and alignment of SP along the slit and in the direction of scanning with respect to NFI.

SP data is scanned on the FOV with 101 steps (slit position: -1000~1000 at intervals of 20). We select one wavelength of SP and make an image that has 101x1024 pix size.

This figure indicates an NFI image that is scanned on the FOV of NFI 6302A image with 101 uniform steps at intervals of 20.

SP data

NFI data

1024

pix

0

1

2

3

4

5

・・・

101

101 pix

FOV

According to these figures, the scanned steps of SP are non-uniform and the plate scale of SP and NFI is different because of …

・・・・・・・・・

(1) Distortion of NFI image

-1000

-500

0

500

1000

(2) Rotation

(3) Uniformity of scanning steps


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of SP images Spectro-Polarimeter (SP), image scale

(1) distortion of NFI image

From NFI image, we can see it distorted by analyzing details. So, we compared

observed grids with even interval grids.

even interval grids


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of SP images Spectro-Polarimeter (SP), image scale

(1) distortion of NFI image

Figure shows the degree of distortion of NFI as a function of a distance from the central point (1023.5, 511.5) of the image.

Distortion is larger near the edge of FOV.

r+dr

(obs.)

r

(even interval grids)

(r+dr)/r

(2) rotation

r

The NFI image is rotated with respect to SP. The angle is 0.2 degree counterclockwise.

NFI

0.2°

It is needed to correct when we analyze the data.

SP


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of SP images Spectro-Polarimeter (SP), image scale

SP data

(3) uniformity of scanning steps

Using vertical lines, we examined the position on NFI image of each slit of SP. The result is shown.

According to these figures, we can see

the non-uniformity of scanning steps

--- the periodic residual component.

To measure them with higher accuracy, it is necessary to analyze data having smaller step size than 20 steps.

NFI data

These results in this presentation are obtained with the data set in May 2005. We have new data set in 2006 with new optical system. We are analyzing them and the new results will be shown in the next time.


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Summary Spectro-Polarimeter (SP), image scale

We know the platescale and displacement of each filter,

it is possible to align all data each other.

FG

SP

BFI

NFI

5550

5576

distortion

rotation

3883

4504

5172

6302

6302

3968

6684

5250

6563

4305

5896

alignment (platescale, displacement)

There is a remaining issue: “absolute platescale.”


Internal alignment between filtergram fg and spectro polarimeter sp image scale

displacement Spectro-Polarimeter (SP), image scale

platescale

X

X

Y

Y


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(BFI)

40 pix

  • Determine grid positions for each filter

  • Plot relative shifts of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image

integration of intensity along the vertical axis on each horizontal point

2nd order fitting

(to an accuracy of better than 0.1 pixel)


Internal alignment between filtergram fg and spectro polarimeter sp image scale

Relative alignment of FG images Spectro-Polarimeter (SP), image scale

(BFI)

  • Determine grid positions for each filter

  • Plot relative shifts of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image

8 pix circle

(1013, 478)

grid center


Internal alignment between filtergram fg and spectro polarimeter sp image scale

(192, 720) Spectro-Polarimeter (SP), image scale

(463, 730)

(733, 739)

(1003, 748)

(1274, 758)

(1544, 767)

(1815, 777)

(202, 450)

(473, 459)

(743, 469)

(1283, 488)

(1554, 497)

(1825, 506)

(211, 179)

(483, 188)

(753, 198)

(1023, 207)

(1293, 217)

(1563, 226)

(1834, 235)

Relative alignment of FG images

(BFI)

  • Determine grid positions for each filter

  • Plot relative shifts of the grid positions with respect to the positions on the 5550A image

  • Calculate average displacements (DX, DY) between two filters by averaging the relative shifts of the grid positions

  • Correct the average displacements, and then plot the grid positions again

  • Get difference of the pixel scale among the images with respect to the 5550A image

8 pix circle

(1013, 478)

grid center